The first thing to consider is are you building this as an MVP or are you digitizing a business where you are already offering this service successfully offline.

Ultimately you get what you pay for and if you go down the cost-effective route initially MVP style you will need to rebuild at a later date.

If you're replicating an existing business that you are digitizing it would probably be worthwhile to use cost effective developers and more of a prototype approach.

Based on the description of what you are doing I am going to assume you are looking to develop an MVP:

1. Using WordPress - using existing theme (free) or use a designer on Upwork/PPH to create a design and wireframes (~ +/- $1k). Use existing membership/payment plugins (cost as per use), use developer to customise and bring everything together $2-5k. With this solution there it is likely there will still be manual operations to do in background as it is difficult to customise word press 100%

2) Using no-code solution like Bubble. This is a fast and easy way to create web and mobile applications. There is a learning curve which can be quite steep depending on what you want to do. The cost for this is $0 except for your time, depends if you are time poor or could be working on something delivering more value. You may need to use a professional for more complex customisations and integrations cost for this tbd depending on what you want to do.

3. Build from scratch - create a business and requirement document/user stories. Post on Upwork, PPH or similar. Talk through with a few bidders, this will help you get your idea to a more advanced stage and may also uncover things you haven't thought of. Estimated cost for an MVP $5k-$40k

Time to launch for all the above would be 2-4 months estimated for a basic stripped back MVP.

I have gone through this process many times when building MVPs and businesses, there is, unfortunately, no fixed way, it will depend on your situation.

Good luck!

Laurent